Dynamic Modelling for the Design of Head-Neck Load Carriage Systems

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Hetzler, Markus
Multibody Dynamics , Head-neck Modelling , Neck Pain , Head-neck Simulation
Head load-carriage systems have broad application, allowing people to carry awkward or heavy loads, but can cause chronic pain when the neck is loaded improperly. Studies have identified military helicopter crew neck pain as a significant issue, with reported incidence of neck pain amongst Canadian flight crews in excess 70% [1][2][3], leading to high costs and operational downtime. Although the problem is multi-factorial, one area of interest is due to the adoption of helmet mounted night-vision goggles, which create large, unbalanced moments on the neck. While no single point solution has been identified, research has ranked external neck support devices fourth out of twelve recommended measures, following education, exercise, and workload distribution, that could have the greatest benefit to reducing neck pain, with an estimated efficacy of 66.1%[4]. The objective of this study was to develop a simplified multibody dynamics (MBD) model to evaluate the C7-T1 moments in flexion-extension (down-and-up motion of the head) and in yaw (side-to-side rotation of the head) for a series of visual scanning tasks. Three base head load conditions were considered: the head-only, a head and helmet, a head and helmet with night-vision googles and battery pack. The model was used to evaluate three potential countermeasures in effort to return the neck moments to the baseline condition (head and helmet). The countermeasures evaluated were: a counterweight, a single line-of-action spring system, and a dual line-of-action spring system. The model demonstrated that the counterweight solution provides increased moments in virtually all situations except for the neutral posture, which is unlikely to reduce long-term injury risk. In contrast, both spring systems have potential to return the flexion moments to the baseline, however these suffer from a restorative moment when the head is rotated in yaw. The potential for improvement however is significant, and the results show further development of implementable solutions is merited. Further work should also be performed to upgrade the MBD model to include a broader set of environmental and task-based loading conditions, and to improve the treatment of variability such as differences in base geometry and how the head-to-helmet connection is simulated.
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